The present invention relates generally to antenna assemblies for wireless communication devices and systems, and in particular to slot antenna assemblies. The invention provides particular utility to dual polarization slot antennas for use telecommunications devices, or other wireless devices, and in wireless local area network systems.
There is a growing need for a structurally compact, resonant antenna assembly for efficient operation over a variety of frequency ranges including, for example, the wireless LAN frequencies. A further need exists for such an antenna to be suitable for mounting within a communication device and yet have little or no operational interference from other internal components of the device. In addition, there is a need for such antennas to have robust hemispherical coverage while minimizing external interference.
Existing antenna structures for wireless devices include both external and internal structures. External single or multi-band wire dipole antennas are half wave antennas operating over one or more frequency ranges. The typical gain is +2 dBi. These antennas have no front to back ratio and therefore radiate equally toward and away from the user of the wireless device without Specific Absorption Rate (SAR) reduction. LC (inductor and capacitor) traps may be used to achieve multi-band resonances. The bandwidth near the head is limited to 80 degrees nominal.
Another external antenna structure is a single or multi-band asymmetric wire dipole. This antenna is a quarter wave antenna operating over one or more frequency ranges.
The typical gain is +2 dBi. There is no front to back ratio or SAR reduction. LC traps may be used to achieve multi-band resonances. An additional quarter wave conductor is needed to achieve additional resonances. The beamwidth near the head is limited to 80 degrees nominal.
Internal single or multi-band antennas include asymmetric dipole antennas. These antennas include quarter wave resonant conductor traces, which may be located on a planar, printed circuit board. These antennas operate over one or more frequency ranges with a typical gain of +1 to +2 dBi, and have a slight front to back ratio and reduced SAR. These antenna structures may have one or more feedpoints, and require a second conductor for a second band resonance.
Another internal antenna structure is a single or multi-band planar inverted F antenna, or PIFA. These are planar conductors that may be formed by metallized plastics. PIFAs operate over a second conductor or a ground plane. The typical gain for such antennas is +1.5 dBi. The front to back ratio and SAR values are dependent of frequency.
An antenna assembly having a resonator structure generally vertically aligned relative to a ground plane, such as the printed wiring board of a wireless communications device, is described. One side of the resonator structure includes a slot resonator circuit structure and a matching stub. The slot antenna assembly of the present invention is useful in cellular telephones and other wireless devices benefiting from a compact and yet robust antenna which radiates with multiple polarizations in various multiple orientations. Additionally, the antenna assembly may be used with such devices with minimal operational interference.
The antenna assembly may also include the following properties: a size suitable for integration within a wireless communications device, such as a cellular telephone, preferably at an upper rear portion of the device; minimization of operational interference from internal components of the device; robust hemispherical coverage; and enhanced performance at selected wireless frequency ranges, preferably 2.4-2.5 GHz, and 1.575 GHz (GPS).
Another object of the invention is to provide an antenna integrated upon a transceiver printed wiring board for ease and economy of manufacture. In one embodiment, an improved slot resonator antenna structure is provided for use with cellular telephones, LANs, personal data devices, and other wireless communication devices. The antenna assembly is of a compact size suitable for mounting directly upon a printed wiring board.
The orthogonal slot antenna assembly of the present invention also preferably includes a conductive ground structure, which may be the printed wiring board of the wireless device.
Other objects and advantages will in part be obvious and will in part appear hereinafter, and will be accomplished by the present invention which provides an omni-directional dual linear and/or elliptical polarization slot antenna structure capable of being mounted on a printed wiring board. Electronic circuitry which receives and/or transmits RF signals may also be mounted to the wiring board. Typically, the electronic circuitry will also include an electronic circuit or network to match the impedance between the antenna and the receiving/transmitting circuitry.
The antenna has a two dimensional, nearly omni-directional pattern, able to communicate using vertical and horizontal polarization signals with reasonable gain. The antenna exhibits the two dimensional nearly omni-directional pattern without using complex structures such as arrays or two slots in a cross pattern. The slot antenna structure includes two resonator arms which are parallel to each other and coupled together via a conductive connection. The design requires only a single feed point connecting the transceiver to the antenna, thus greatly simplifying the structure and reducing the cost compared to arrays or cross slot antennas.
The antenna assembly may be disposed away from the ground plane of an associated wireless communications device and coupled via a signal transmission line such as an RF coax line, a microstrip transmission line, a coplanar wave guide, or other known signal transmission approaches as appreciated by those skilled in the arts.